The Internet provides access to a wide variety of resources. For example, video, audio, and Web pages are accessible over the Internet. These resources present opportunities for other content (e.g., advertisements, or “ads”) to be provided along with the resources. For example, a Web page can include slots in which ads can be presented. The slots can be allocated to content providers (e.g., advertisers). An auction can be performed for the right to present advertising in a slot. In the auction, content providers provide bids specifying amounts that the content providers are willing to pay for presentation of their content.
Content may be selected for an auction based on a match of one or more input tokens (e.g., keywords) to tokens associated with the content. For example, an ad for sports memorabilia may be associated with the keywords “baseball”, “football”, and “basketball”. If a user inputs one of those keywords into a search engine, the input keyword may be matched to a keyword associated with the ad, resulting in the ad being selected for auction. In some cases, there need not be an exact match between keywords that are input and keywords that are associated with content in order for that content to be selected for auction.